President Donald J. Trump delivers his Inaugural address after taking the oath of office as the 45th President of the United States in Washington. (Shawn Thew/EPA)

President Trump began his dark and forceful inaugural speech by addressing the Chief Justice of the United States, the four former presidents in attendance, his "fellow Americans" and one other group: the "people of the world."

Though it was an unusual start for an inaugural address -- no president since Richard Nixon in 1969 has addressed his "fellow citizens of the world community" -- it was an apt inclusion, particularly for a staunchly nationalist, "America First" speech.

"From this day forward, a new vision will govern our land," Trump said in his remarks. "From this day forward, it's going to be only America first, America first."

Inaugural speeches tend to be remembered for their soaring rhetoric aimed at unifying a nation after it's endured the divisions that emerge in a campaign season. And indeed, until Friday's address -- one that sounded more like a stump speech to his campaign supporters and in which Trump said "this American carnage stops right here and stops right now" -- that has been their most common purpose. From Thomas Jefferson’s first inaugural (“we are all Republicans, we are all Federalists”) to John F. Kennedy’s address (“ask not what your country can do for you …”), the most memorable lines are directed broadly at Americans -- of shared values and the ways they're united in a democracy.

But the outside world is another audience for the inaugural speech that often gets less attention. Unlike the State of the Union address (often a laundry list of legislative priorities), or a farewell address (an opportunity to reflect or recap), presidents have used their inaugural addresses to send a signal to the world community about the new presidency.

People often forget this, says Kathleen Hall Jamieson, a professor at the University of Pennsylvania’s Annenberg School of Communication who studies presidential rhetoric. “The world is envisioned differently in inaugurals than in other speeches," she says. "The only other time the world is invited into the speech, writ large, is when the president makes an invitation to Congress to declare war.”

During his 1917 second inaugural speech, for instance, Woodrow Wilson memorably declared "we are provincials no longer." A month later, he asked Congress for a declaration of war on Germany. John F. Kennedy's speech is best remembered for his "ask not" line, but just as important was his commitment that the United States "shall pay any price, bear any burden, meet any hardship, support any friend, oppose any foe," a warning to Russia from a young president that in hindsight is viewed in the context of Vietnam.

Trump spoke to the broader world not only with his opening, but with a thread of nationalism that ran throughout his campaign and his speech. He derided the enriching of "foreign industry at the expense of American industry" and subsidizing "the armies of other countries," defending "other nations' borders while refusing to defend our own."

Aaron Kall, who directs the University of Michigan's debate program and has edited a book on inaugural addresses, says "that’s a very isolationist" view at a time when "the world is so interconnected." Yet he notes the populism of it -- that it is clearly a "politically persuasive message to some who are asking 'how do I pay for my groceries?' "

Trump promised that "every decision on trade, on taxes, on immigration, on foreign affairs will be made to benefit American workers and American families. We must protect our borders from the ravages of other countries making our products, stealing our companies and destroying our jobs. Protection will lead to great prosperity and strength," adding "we will follow two simple rules: buy American and hire American."

Jamieson said that the inclusion of the word "protect" is unclear. While it appears to read plainly like a statement about trade, she notes, the inclusion of foreign affairs and the use of "protection" rather than "protectionism" could also be read as a statement about military strength in the fight against ISIS. "He's either using calculated ambiguity or it wasn't written carefully," she said.

Trump went on to say "we will seek friendship and goodwill with the nations of the world, but we do so with the understanding that it is the right of all nations to put their own interests first," promising to "reinforce old alliances and form new ones and unite the civilized world against radical Islamic terrorism, which we will eradicate from the face of the Earth."

While that reinforcement of alliances may be reassuring to some in the world -- particularly in light of reports this week where he called NATO "obsolete" -- combined with the "America First" rhetoric and the frequent references to winning, "it says we're in a zero-sum game," says Jamieson, one that moves away from the "community of nations" rhetoric. "Winning implies losing. A foreign nation's leader can read this as saying we're going to accomplish all these things at the expense of the rest of the world."